This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The aim of this study is to more accurately assess the effects of vitamin D replacement on inuslin sensitivity and beta-cell function in vitamin D deficient subjects who have impaired fasting glucose (serum glucose of 100-125 mg/dl after a 12 hour fast) and/or impaired glucose tolerance (serum glucose between 140-200 mg/dl 2 hours after 75 gram gluocose load).